Silicon dioxide layers are widely used in the semiconductor industry as dielectric layers and passivation layers. Said layers are commonly provided by means of a LPCVD-process (As used herein, LPCVD means low pressure chemical vapour deposition). Such SiO.sub.2 layers are also used in optical filters, the so-called interference filters. Low pressure is to be understood to means herein a pressure between 10.sup.-5 and 1 bar.
In such a process it is important for the reaction velocity to be kinetically controlled, which means that the reaction velocity is highly temperature-dependent. In that case, the SiO.sub.2 layer formed has a uniform layer thickness and an excellent step coverage takes place. The latter property is important, in particular, in VLSI-applications in which complex geometries having dimensions of approximately 1 .mu.m must be provided with a SiO.sub.2 layer having a uniform thickness.
The opposite of kinetically-controlled reactions is formed by diffusion-controlled reactions. Diffusion-controlled reactions or processes generally lead to a poorer uniformity of the layer thickness, measured both on one substrate and on different substrates in one batch. It has been found that a satisfactory uniformity can be obtained when the activation energy of the reaction exceeds 100 kJ/mol.
A method of providing a silicon dioxide layer on a substrate by LPCVD is described in British Patent Application UK-A 2061243. In the method described therein, a SiO.sub.2 layer is formed by a reaction of silane (SiH.sub.4) or dichlorosilane (SiH.sub.2 Cl.sub.2) with an oxidizing agent such as NO or N.sub.2 O.sub.4. The reaction takes place in the temperature range between 430.degree. and 633.degree. C. at a pressure of approximately 1 mbar. The activation energy of the reaction with N.sub.2 O.sub.4 is 0.91 eV/molecule, which corresponds to 87.4 kJ/mol. Said British Patent Application makes no mention of the measured layer thickness on different substrates in one batch, nor does it mention the degree of step coverage.
In another known LPCVD-process, TEOS (tetraethyl orthosilicate) is used. This reaction is kinetically controlled, however, the process temperature must be at least 650.degree. C. This means that the process is unsuitable for the application of a SiO.sub.2 -layer on aluminum and many silicides. Moreover, in this instance, glass cannot be used as the substrate. Another low-temperature process is based on, for example, DES (diethyl silane), however, said reaction is diffusion-controlled, which leads to a poor uniformity of the layer formed. An example of a kinetically-controlled, low-temperature LPCVD-process is a process which is based on DADBS (diacetoxy ditertiary butoxysilane). The layers formed have a satisfactory uniformity of the layer thickness, however, the deposition rate at 450.degree. C. is only 2 nm/min. Besides, the SiO.sub.2 -layers formed exhibit a shrinkage of approximately 20% after annealing.